It is known that acrylonitrile can be produced from propylene in various processes in which propylene is brought into contact with molecular oxygen and ammonia in a gas phase in the presence of a catalyst at an elevated temperature. These processes are known as catalytical ammoxidation processes for propylene. This ammoxidation of propylene can be effected only in the presence of a catalyst. U.S. Pat. No. 2,904,580 disclosed, for the first time, a P-Mo-Bi-O type catalyst effective for the ammoxidation of propylene. After this U.S. patent, various types of catalysts were provided for the ammoxidation process for propylene. For example, U.S. Pat. Nos. 3,226,422, 3,254,110, 3,641,102 and 3,746,656 and Japanese Patent Application Publication (KOKOKU) No. 45-35287(1970), respectively, disclosed an Fe-Bi-Mo-P-O type, an Fe-Ni-Mo-P-O an Fe-Bi-Mo-P-O type, an Fe-Ni-Mo-P-O type, a Te-Mo-Fe-O type, a Tl-P-Mo-Fe-Bi-Mg,Co and/or Ni-O type and a P-Mo-Bi-Ni-,Co,Zn and/or Sn-O type catalyst, each of which is effective for the process of producing acrylonitrile from propylene. Also, Japanese Patent Application Laying-open (KOKAI) No. 49-108018(1974) disclosed a Co-Fe-Bi-W-Mo-Si-Tl, alkali metal and/or alkaline earth metal-O type catalyst useful for the ammoxidation process for propylene.
However, when the above-mentioned types of conventional catalysts are used in the process for producing acrylonitrile by the ammoxidation of propylene, the following disadvantages are exhibited.
1. The catalytical ammoxidation reaction temperature at which acrylonitrile can be produced at the highest yield is about 450.degree. C., which is undesirably high. This undesirably high reaction causes the durability in catalytic activity of the catalyst to be shortened and undesirable side-reactions to be promoted.
2. The reaction time (contact time) necessary for producing acrylonitrile at a high yield is undesirably long. The undesirably long reaction time results in the same disadvantages as those of the undesirably high reaction temperature.
3. The space time yield of acrylonitrile is undesirably low. This undesirably low space time yield of acrylonitrile causes the catalyst to be consumed in a large amount and the production cost of acrylonitrile to be high.
Also, when the above-mentioned conventional catalyst is used to convert propylene into acrylonitrile under a certain reaction condition which is effective for carrying out the reaction at a high percent conversion of propylene, sometimes such a reaction condition causes the reaction to exhibit a reduced percent of selectivity to acrylonitrile and a poor percent of yield of acrylonitrile, even if the catalyst is effective for producing acrylonitrile at a high percent selectivity thereto under another reaction condition.
Some of the conventional catalysts containing molybdenum, bismuth, iron and cobalt and/or nickel are effective for producing acrylonitrile at a high percent of yield thereof.
However, some of the bismuth-containing catalysts exhibit a disadvantage in that the necessary reaction temperature is undesirably high, the necessary reaction time is undesirably long, and the space time yield of acrylonitrile is undesirably low. Accordingly, it is desired to modify the conventional bismuth-containing catalysts so as to make possible the production of acrylonitrile from propylene at a high percent of conversion of propylene, at a high percent of selectivity and a high percent of yield of acrylonitrile, at a high space time yield of acrylonitrile, at a relatively low reaction temperature during a relatively short reaction time and at a low cost.
U.S. Pat. No. 4,070,390, having the same inventors as of the present invention, disclosed a new Mo-Bi-Fe-Co-V and/or Te-O type catalyst effective for producing acrylonitrile from propylene. This catalyst contains bismuth in a very small amount of from 0.01 to 0.7 atoms per atom of molybdenum. However, this catalyst is capable of ammoxidizing propylene within a short reaction time of about 1.7 seconds, at a low reaction temperature of about 400.degree. C., at a high percent of conversion of propylene and at a high percent of selectivity to acrylonitrile. Therefore, this catalyst can produce acrylonitrile at a high yield of 80% or more, at a high space time yield of 250 g/l of catalyst.hour or more. It has been found, however, that this catalyst exhibits such a disadvantage that the reaction product contains a relatively large amount, about 3% by weight, of acrolein as a by-product. This acrolein causes some difficulties in the refining process of the reaction product. That is, acrolein is easily polymerized in the reaction product and the polymerized acrolein adheres onto the inside surface of the reaction equipment. Also acrolein easily reacts with hydrocyanic acid, which is contained as a by-product in the reaction product, and which is useful as a material for producing acetocyanohydrin, to produce acrolein cyanohydrin. Accordingly, it is difficult to recover the hydrocyanic acid from the reaction product. Furthermore, the reaction product contains acrylic acid as a by-product. The acrylic acid is readily polymerized and the resultant polymer undesirably deposits on the inside surface of the reaction equipment. Also, the catalyst of U.S. Pat. No. 4,070,390 exhibits such a disadvantage that, even if the catalyst is shaped into tablets by using a tablet-forming machine, the resultant tablets exhibit a poor crushing strength. Accordingly, when used in a practical process, the tablets of the catalyst are readily deteriorated, divided into fine particles and/or worn down.
British Pat. No. 1,436,475, having the same inventors as the present invention, disclosed a Mo-Bi-Fe-Co-W-Ca-Ti-O type catalyst useful for the production of acrylonitrile from propylene. This catalyst can be shaped into tablets having an excellent crushing strength. The composition of this catalyst is effective for preventing the loss of molybdenum from the catalyst and the deterioration, crushing and/or wearing of the catalyst during reaction. Also, the catalyst is effective for producing acrylonitrile at a high yield thereof. However, the catalyst exhibits such disadvantages that the reaction product contains a relatively large amount of acrolein as a by-product, that the necessary reaction time is undesirably long, that is, about 3 seconds and that the space time yield of acrylonitrile is unsatisfactorily low.